Encyclopedia of Espionage, Intelligence, and Security

Underground Facilities, Geologic and Structural Considerations in the
Construction

█ WILLIAM C. HANEBERG

Natural and manmade underground facilities have played an important role
in warfare and national security for more than 5000 years. Underground
chambers were used for hiding places and escape routes in Mesopotamia and
Egypt from 3500 to 3000
B.C.,
and they continue to play an important role in the ongoing conflict in
Afghanistan. Some notable twentieth-century uses of underground facilities
for warfare and national security include dozens of underground factories
constructed beneath Germany during World War II; the Cheyenne Mountain
Operations Center, Colorado; as many as 1000 underground facilities
estimated to exist beneath the Korean Demilitarized Zone; and countless
natural and manmade caves used by al-Qaeda forces in Afghanistan. Large
manmade cavities in salt domes along the Gulf Coast, some of them larger
than 17 million cubic meters in volume, are used for the United States
Strategic Petroleum Reserve. The details of underground facilities used
for military or national security purposes are classified, but there is no
reason to assume that they are not on the scale of underground civil
projects. The largest unsupported span ever constructed in rock was a 61 m
(200 ft) wide hockey arena constructed for the 1994 Winter Olympics in
Norway, and underground mines in many parts of the world consist of
smaller passages that extend for many miles.

Extensive underground facilities have also been constructed to maintain
communications and house the United States government in the event of an
attack. An underground facility known as Site R exists within Raven
Mountain, Pennsylvania, and is thought to have been the location from
which Vice President Cheney and other officials worked in the aftermath of
the September 11, 2001 terrorist attacks. Construction of Site R was
authorized by President Truman and completed during the early 1950s.
Declassified information dating from the construction period describes a
three-story underground facility with more than 18,000 square meters of
floor space and room for more than 5000 people. The existence of another
extensive underground facility beneath the Greenbrier Resort in West
Virginia, constructed to house the United States Congress in the event of
a nuclear attack, was made public in 1992.

Although they can be expensive and difficult to construct, underground
facilities offer two important advantages over surface structures. First,
they are almost completely hidden from view and activities within them can
be invisible to even the most sophisticated intelligence satellites.
Second, their depth can make them resistant to conventional and some
nuclear attacks. Additional advantages include lower long-term maintenance
costs (because underground structures are not exposed to weather) and
lower heating and cooling costs (because temperature is constant in
underground environments). The detection and characterization of
underground facilities and the development of technologies to defeat
hardened underground facilities are among the principal goals of modern
military geologists.

Geologic factors exert an important influence on the design and
construction of any underground facility. One of the most important
factors is the strength of the soil or rock into which underground
structures are excavated. Shallow underground structures can be
constructed in soil or highly weathered rock using a technique known as
cut-and-cover construction. These structures are built by first excavating
a hole, then building the desired facilities, and finally covering the
completed structures with soil. Because soil and weathered rock near
Earth's surface tends to be weak, shallow cut-and-cover structures
must be heavily reinforced with concrete or other materials if they are to
withstand attack. The mineral quartz, which can be a common component of
the rocks that are used for concrete aggregate, changes volume when it
undergoes a phase transition at high temperatures (844 degrees K at a

A car enters the U1a Complex, an underground facility in Nevada
designed for conducting subcritical experiments to determine whether
aging nuclear weapons remain reliable and safe.

AP/WIDE WORLD PHOTOS

.

pressure of 0.1 MPa). In order to prevent thermal disintegration,
therefore, aggregate for concrete that may be subjected to extremely high
temperatures must consist of rocks containing little quartz. Cut-and-cover
structures can be difficult to hide during construction, when they can be
easily pinpointed on remote sensing images or aerial photographs. It may
also be possible to locate shallow cutand-cover structures after
construction if soil disruption or activity within the structure produces
a thermal, soil moisture, or soil chemistry anomaly identifiable through
multispectral or hyperspectral image analysis.

Deep underground facilities can be constructed using specialized tunnel
boring machines (TBMs) or by underground drilling and blasting. These
construction techniques are used extensively in the underground mining
industry and the construction of civil works such as tunnels. Tunnel
boring machines are large pieces of construction equipment with faces that
consist of rotating cutting tools, allowing the machine to drill itself
into earth or rock and create tunnels many meters in diameter. Underground
construction by drilling and blasting begins with a carefully designed
pattern of holes drilled into a rock face. The holes are loaded with
explosive charges that are detonated according to a specified sequence in
order to efficiently fracture and loosen the rock, which is then removed
to expand the underground opening.

The primary geologic factor controlling underground construction in rock
is the nature of the rock itself. Strong rock with uniform physical
properties is the preferred choice for underground construction.
Clandestine tunnels excavated beneath the Korean Demilitarized zone by
North Korea, for example, tend to be located in granite that is relatively
uniform and contains few fractures rather than adjacent rocks that are
more highly fractured. Depending on the geologic setting of an underground
facility, selecting choice rock may not be an option. Rocks are commonly
heterogeneous, with physical properties such as strength and degree of
natural fracturing varying from place to place.

Engineering geologists and civil engineers commonly describe the physical
quality of rock using a simple parameter known as the Rock Quality
Designation, or RQD, which is obtained by measuring core samples obtained
during exploratory drilling prior to construction. The RQD is the
percentage of pieces of core sample longer than 10 cm (4 in) divided by
the total length of core. Thus, a core sample of intact rock with no
fractures or cracks would have an RQD of 100. A core sample of highly
fractured rock in which only one-quarter of the pieces are longer than 10
cm would have an RQD of 25. Other factors that affect the design and
construction of underground facilities in rock include the number and
density of natural fractures in the rock, the roughness of fracture
surfaces and the degree of natural chemical alteration along fracture
surfaces (both of which affect rock strength), the presence or absence of
water in the fractures, and the presence or absence of zones of weakness
such as faults or rock that has been altered to the consistency of clay.
Highly fractured rock near a large fault, for example, may be too weak to
support itself above an underground cavity or serve as a conduit for
high-pressure water that can quickly flood an underground opening.
Completion of the NORAD underground facility in Cheyenne Mountain during
the 1960s, for example, was delayed for more than a year because of
problems with a geologic fault intersecting the ceiling of the
underground opening. Underground openings in weak, highly fractured, or
water saturated rock can be lined with reinforced concrete or shored with
steel beams in order to ensure the safety of construction workers and
later occupants of the space. The lithostatic stress that must be resisted
by underground openings of any size increases linearly with depth, and the
most stable underground openings are generally circular or spherical.
Rectangular or cubic openings contain sharp corners that concentrate
stresses in the rock and can lead to the collapse of the opening.

One issue that is important for military or securityrelated underground
facilities, but generally not for civil structures, is their vulnerability
to attack by conventional or nuclear weapons. The vulnerability of an
underground facility to a conventional weapon attack is a function of its
depth, the strength of the overlying rock, and the penetrability of the
soil or rock exposed on Earth's surface above the facility.
Knowledge of these properties is essential to those designing facilities
to survive attacks as well as to those designing specialized earth
penetrating weapons (EPWs). The geologic information necessary to evaluate
the vulnerability of a facility has been given the name "strategic
geologic intelligence" by some military geologists. Few, if any,
underground facilities can withstand a direct nuclear attack.